开特（katal,符号kat）系计量催化剂（比如酶）催化力的派生国际单位。国际计量大会等国际组织推荐使用该单位。与该单位类似的是非国际单位酶单位（enzyme unit），尽管后者在生物化学等领域中使用频率更高。

开特并不用来表示反应的快慢。反应快慢是用浓度/时间来表示的。开特是用于表示催化剂的催化力的单位。开特（在催化剂活力不受影响的情况下）应为一个不变的值，但测得的值却会发生变化，且与实验时的环境条件有关。因此，为了定义催化剂的催化活力，开特以mol/s作为单位。比如，一开特的胰蛋白酶是指可以在1秒内消化1mol肽键的胰蛋白酶的量。

The katal (symbol: kat) is the SI unit of catalytic activity. It is a derived SI unit for quantifying the catalytic activity of enzymes (measuring the enzymatic activity level in enzyme catalysis) and other catalysts. Its use is recommended by the General Conference on Weights and Measures and other international organizations. It replaces the non-SI enzyme unit. Enzyme units are, however, still more commonly used than the katal in practice at present, especially in biochemistry.